linux-kernel - Re: [PATCH v1 1/7] virtio-gpu api: add blob userptr resource

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Message-ID: <4b749976-9589-491c-995e-36cfbd02cd61@collabora.com>
Date: Sun, 30 Mar 2025 14:57:00 +0300
From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
To: Demi Marie Obenour <demiobenour@...il.com>,
 "Huang, Honglei1" <Honglei1.Huang@....com>, David Airlie
 <airlied@...hat.com>, Gerd Hoffmann <kraxel@...hat.com>,
 Gurchetan Singh <gurchetansingh@...omium.org>, Chia-I Wu
 <olvaffe@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Simona Vetter <simona@...ll.ch>, Rob Clark <robdclark@...il.com>,
 Huang Rui <ray.huang@....com>
Cc: dri-devel@...ts.freedesktop.org, virtualization@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/7] virtio-gpu api: add blob userptr resource

On 3/29/25 22:50, Demi Marie Obenour wrote:
> On 3/26/25 10:46 AM, Dmitry Osipenko wrote:
>> On 3/6/25 13:51, Huang, Honglei1 wrote:
>>>
>>> On 2025/3/1 5:21, Demi Marie Obenour wrote:
>>>> On 2/28/25 12:36 AM, Honglei Huang wrote:
>>>>> From: Honglei Huang <Honglei1.Huang@....com>
>>>>>
>>>>> Add a new resource for blob resource, called userptr, used for let
>>>>> host access guest user space memory, to acquire buffer based userptr
>>>>> feature in virtio GPU.
>>>>>
>>>>> - The capset VIRTIO_GPU_CAPSET_HSAKMT used for context init,
>>>>> in this series patches only HSAKMT context can use the userptr
>>>>> feature. HSAKMT is a GPU compute library in HSA stack, like
>>>>> the role libdrm in mesa stack.
>>>>
>>>> Userptr should not be limited to HSMKMT contexts.  Userptr can
>>>> accelerate shm buffers by avoiding a copy from guest to host, and
>>>> it can be implemented using grant tables on Xen.
>>>
>>> Yes, I totally agree userptr can accelerate shm buffers, but I currently
>>> don't know if there are any other projects working on similar features,
>>> or if maintainers have any opinions or better ways to implement them, so
>>> I temporarily limit this feature to HSAKMT context only.
>>>
>>> I am waiting for everyone's opinions, please provide your thoughts.
>>
>> USERPTR should be relevant for anything Vulkan-related, like Venus and
>> native contexts. I expect that this new feature will work universally
>> good for all context types.
>>
>> In order to merge USERPTR support upstream, we at least will need to
>> prototype the guest USERPTR in one of native context driver to know that
>> it works. You'll need to post the whole set of host/guest USERPTR
>> patches including QEMU and etc, not just the kernel patches.
> 
> Does the user-mode VMM need to be QEMU or would patches to
> another open-source VMM, such as crosvm, be sufficient?

General-purpose features should be made supported by QEMU when possible.
Testing feedback for other VMMs will be very valuable too.

-- 
Best regards,
Dmitry